Modern turbomachines are conventionally produced in the form of an assembled collection of modules. They first of all comprise one or more compressor modules arranged in series and which compress air drawn into an air inlet. The air is then let into a combustion chamber where it is mixed with a fuel and burnt. The combustion gases pass through one or more turbine modules which drive the compressor or compressors. The gases are finally discharged either into a jet pipe nozzle to produce a propulsive force or onto a free turbine to produce power which is recovered on a transmission shaft.
These modern turbomachines, because of the high temperatures of the gases leaving the combustion chamber, are cooled, which means to say that a fresh-air ventilation circuit is installed in order to cool the metal of the turbine vanes when the turbomachine is operating. The ventilation air is bled off the outlet side of the compressor stages and conveyed to the turbine. The air generally enters via the root of the vanes, passes through these vanes via cavities cut into the thickness of the blade and is then discharged through perforations made in the wall or tip of the vanes. The cavities are formed longitudinally inside the vanes, extending between the root and the tip of the vane, so as to carry this air and cool the metal. In general, several cavities are positioned one beside the other along the chord of the vane, so as to equalize the flow rates and cool the metal uniformly.
Various types of dust (particularly fine sand) may be drawn into the air intake at the same time as the air needed for the operation of the engine. While most of the dust passes through the engine without causing any damage, some of it reaches the turbine vane cooling circuits; if it builds up inside these circuits there is then the risk of it blocking the cavity outlet discharge orifices and thus endangering the integrity of the vane. To prevent this from occurring, turbine vanes are equipped with calibrated dusting holes in addition to the cooling drillings and vents, these dusting holes being situated at the tops of the cavities and having the role of removing the dust.
Dusting holes are installed for each of the cavities. The sizing of the hole is dictated by criteria concerned with the size of the dust and is therefore independent of the overall size of the vanes. Installing a dusting hole in the case of a small-sized vane proves to be particularly tricky and may become a decisive factor in the sizing of the circuit because it is likely to govern the thermal performance of the cooling circuit.
The problem that has to be addressed is a particularly acute one in the case of a high pressure (HP) turbine vane the size of which is very small and in which the cavity that cools the trailing edge is of very slender thickness. Installing the trailing edge cavity dusting hole on a short-chord vane may lead to an abnormal increase in the size of this one cavity at the expense of the others. The trailing edge cavity may in such instances represent 25% of the total chord length whereas it usually represents only 15 to 20% on larger vanes. That means that small-sized vanes that have this type of dusting hole will require more cold air to cool them via the trailing edge cavity, at the expense of the cooling using the other cavities. It is therefore important to be able to reduce the cross section of the trailing edge cavity so as to reduce its cooling flow rate and thus be able to maintain a satisfactory overall thermal performance. The problem that has to be addressed in order to achieve this objective is that of finding a way of removing the dust from the trailing edge cavity without installing the dusting hole in the tip of the vane.
It is an object of the present invention to solve these problems by proposing a turbine vane that does not have some of the disadvantages of the prior art and that, in particular, has no trailing edge cavity dusting hole situated in the vane tip. Another object of the invention is to optimize the use of the dusting air, by making it contribute to the cooling of the vane.